Okay, here is the setup - One Linux Fedora machine and three Win XP machines, all machines have broadband internet connections.

Win machines are remote and can communicate with each other and Linux machine only via internet. They have dynamic IPs.

Fedora machine has an external static IP.

Objective is to allow the XPs to access the remote files located on the Fedora machine over internet and work directly on that remote files at block level, with partial file access, and, if possible, more or less unproblematic concurrent access.

As far as I know, the most secure way to do that is to set up a VPN.

Sad part of the story is that it is pretty much the end of what I know.

So here I come, asking if anyone could give me a hand in implementing this setup.

P.S.: offtopic
The Fedora machine is a gift from a Linux affectionado who is a friend of mine. Wanted to inspire me to check out the "real OS"...